Sensors & Software CONQUEST 100, User Manual

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Conquest 100 Principles of Operation
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Some slab-on-grade concrete floors contain fine steel fibers for crack control. The results of
Conquest surveys on these floors vary with the amount and distribution of the metal. Basically,
the more metal fibers, the poorer the penetration and overall results.
2.5.3 Penetration Depth
GPR uses radio waves to image the subsurface. These waves are strongly absorbed by the
material being scanned. The electrical conductivity of the material dictates how deep signals will
penetrate. Concrete can be highly variable depending on the original mix and state of wetting.
Figure 2-8 shows how the depth of penetration can vary with concrete type.
Figure 2-8: Concrete absorbs GPR signals and generally limits penetration to about 24
” (0.6 m).
There is a finite limit on the concrete thickness that can be measured with GPR. Experience
indicates that approximately 24
” (0.6 m) of concrete is the limit of exploration under good
conditions. In most practical scenarios, the presence of rebar or wire mesh, as well as the
constituents of concrete (aggregate, admixtures, and air entrainment) will often result in
penetration that is sligh
tly lower than 24”.
2.6 Power Cable Detection (PCD) Principles
Conquest 100 uses two technologies when imaging concrete for embedded objects: GPR and a
device for detecting current-carrying wires (Figure 2-9) called the Power Cable Detector (PCD).